So called side-mounted agitators are well known in the state of the art. Such agitators are formed of drive means, the propeller and the support means. The drive means comprise an electric drive motor, a reduction gear (with either gear wheels or belt and pulleys) and a propeller drive shaft. There are two options for arranging the electric drive motor and the reduction gear. In a first option the shaft of the drive motor is parallel with the propeller drive shaft, whereby also the shafts of the reduction gear are parallel with the propeller drive shaft. In a second option the electric drive motor is arranged at an angle to the axis of the propeller, normally at right angles to the axis.
An example of side-mounted agitators of the first option is disclosed in U.S. Pat. No. 5,040,899. The propeller drive shaft is normally formed of two parts, i.e. a first part extending out of the reduction gear and a second part actually driving the propeller. The parts are connected to one another by means of a coupling, which may be a flange coupling, a split muff coupling or a sleeve coupling. The support means ensure that the propeller may be taken deep into the mixing vessel without a risk of imbalance and vibrations of the long drive shaft. The support means comprises a support frame extending from a mounting flange, via which the agitator is attached to the wall of the mixing vessel, inside the mixing vessel towards the propeller. The support frame is, preferably but not necessarily, conical for facilitating the liquid flow in the vessel. At one end of the support frame, there is the support bearing, which is located as close to the propeller as practically possible for preventing the propeller shaft from bending and vibrating when in use. The support bearing used in this kind of prior art agitators is a ball or a roller bearing. For protecting the support bearing from the liquid, and especially from the solids in the liquid, to be agitated the space around the propeller shaft between the bearing and the propeller is provided with a shaft seal, which may be a single or double acting mechanical seal, a labyrinth seal or a packing box, just to name a few alternatives. The sealing is, naturally arranged to the extreme end of the support frame facing the propeller.
The agitator is fastened to the wall of a mixing vessel, chest, tower or container of its mounting flange such that the support frame extends through an opening in the wall of the mixing vessel deep inside the mixing vessel, and the drive means, for the most part thereof, remain outside the mixing vessel. Sometimes the mounting flange or the wall of the mixing vessel nearby is provided with two support rails on both sides of the drive means such that the drive means are supported on the rails, and may be pulled along the rails away from the mixing vessel. The US patent teaches that the propeller may be loosened from the end of its drive shaft after the mixing vessel has been emptied whereafter the sealing and the support bearing are accessible from inside the mixing vessel for the maintenance of the bearing and/or the sealing.
A problem relating to this kind of prior art agitators is that the sealing or the bearing at the end of the support frame cannot be replaced or serviced without emptying the mixing vessel. The emptying of the mixing vessel not only takes time but it also interrupts the production or, in the least, causes a risk of severe problems in the production.
Another prior art agitator has been discussed in U.S. Pat. No. 4,511,255. The patent discloses an agitator assembly including a drive shaft extending through a tubular housing. A slide coupling is connected between the outer end of the drive shaft and a drive motor. An impeller is secured to the other end of the drive shaft, which is supported on a bearing/seal member in the inner end of the shaft housing. The adjoining surfaces of the bearing/seal member and impeller base are normally engaged in rotary sealing relationship by springs but shift apart responsive to introduction of cleaning solution into the housing so that the cleaning solution is discharged into the tank at the base of the impeller after washing the seals to facilitate cleaning without manual disassembly or scrubbing. A rotary seal is arranged at the outer end of the shaft but the maintenance of the rotary seal has not been discussed.
A way to repair or to replace the shaft sealing without emptying the mixing vessel is disclosed in the CN utility model document representing the other option for arranging the electric drive motor and the reduction gear, i.e. to arrange the shaft of the electric drive motor at right angles to the propeller drive shaft, whereby the reduction gear is an angle gearbox. This kind of a construction is compact, as it does not require much space in radial direction outside the mixing vessel. However, the construction has some weaknesses, which will be discussed later on. The CN-U-202146735 document discusses an agitator fastened to the side wall of a vessel. The propeller shaft of the agitator extends deep into the vessel such that it is surrounded by a tubular support frame. The support frame is fastened at its first end to a mounting flange used for fastening the angle gearbox to the wall of the vessel. The propeller shaft extends through the angle gearbox and a mechanical seal is arranged in the nearhood of the first end of the shaft such that it is easily accessible when needed, i.e. opposite to the second end of the shaft where the propeller is arranged. For repairing the mechanical seal the propeller shaft is provided at its second end close to the propeller with a plug and a sealing seat that cooperate with the end of the tubular support frame such that when the propeller shaft is pulled outwardly the plug and sealing seat prevent any leakage of the fluid from the vessel along the tubular support. At the second end of the propeller shaft there is also locking means for preventing the rotation of the shaft during maintenance for facilitating the maintenance of the shaft sealing. The locking means are supposed to function such that by pulling and simultaneously rotating the shaft the cogs and grooves of the locking means find one another and lock the shaft immobile in circumferential direction.
The agitator disclosed in the Chinese document has, however, a number of weaknesses or problems in both structural and functional sense. Firstly, at least the document does not explain how the shaft is supported during the repair or replacement of the shaft sealing. The propeller shaft of the agitator discussed in the CN document is driven, and supported by means of a drive member attached to the first end of the shaft, whereby the drive member has to be removed prior to the repair or replacement of the shaft seal at the very same end of the shaft. The document does not give any suggestion to support the shaft somehow, whereby there is a risk that the support bearing at the second end of the shaft gets damaged due to the slightly swinging shaft therein. Also, though it has been discussed that the plug and the sealing seat prevent the leakage when the shaft is pulled outwardly, on the one, it has not been taught how the shaft is kept in its pulled position during the maintenance of the shaft seal, and on the other hand, the slight swinging of the shaft causes minor deflections in the directions of the sealing surfaces, whereby there is a clear risk the seal starts leaking. As to the locking of the shaft immobile in circumferential direction by using locking means situated in the mixing vessel in communication with the liquid being mixed, practice has shown that the user cannot ever be sure that the locking works properly. Very often the fluid in the mixing vessel includes solids or some substances that tend to collect in the grooves of the locking means, whereby the locking cannot be secure. And finally the angle gear itself due to its constructional limitations to a certain reduction range cannot be applied to the full range of electric motors and agitators needed in different mixing applications. Therefore the angle gear should be combined with another reduction gear, which raises the costs of the drive means significantly.